Force lowenergyscanner to show empty list if we did not find services

Previously the UI was only updated when a new service was discovered
on a device. In the extremely rare event of no services being found
the UI was hanging in the "Searching for services" view.

Change-Id: I245216ac4e373a765dea2e182ab541e8830417d0
Reviewed-by: Timur Pocheptsov <Timur.Pocheptsov@digia.com>
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>